The present invention relates generally to Li-ion batteries, and more particularly, to a Li-ion battery having shielded leads to reduce the likelihood of shorting.
Broadly stated, a Li-ion cell is generally comprised of an anode section, a cathode section and a separator layer that is disposed between the anode section and the cathode section. A layer of a first conductive material is disposed within or in contact with the anode section. This layer forms what is conventionally referred to as an xe2x80x9canode current collector.xe2x80x9d A second layer of a conductive material is disposed within or in contact to the cathode section to form a xe2x80x9ccathode current collector.xe2x80x9d It is conventionally known to use metal screens or meshes or foils to form the aforementioned current collectors. Typically, a copper mesh is used to form the anode current collector, and an aluminum metal mesh is used to form the cathode current collector. Current collectors are typically die-cut from sheets of metal mesh, and each current collector includes a tab portion that defines a battery lead. In this respect, an anode current collector will include a tab to define a battery""s negative lead and the cathode current collector will include a tab to define a battery""s positive lead.
A problem with using metal mesh as a current collector is that metal burrs or shards may be formed during the die-cutting process. These burrs or shards project at angles to the plane of the current collector. In the body of the cell, these burrs or shards generally do not create a problem as the layers of metal mesh forming the respective current collectors are generally maintained separate from each other by the respective layers of material forming the cell. However, the tabs forming the electrical leads extend beyond the peripheries of the anode section, cathode section and separator layers and do create a problem of shorting, particularly in a cell having two or more cathodes. In such cells, the leads of the cathode current collectors are typically in registry with each other and are pressed together to form one positive battery lead. Specifically, the aforementioned cells are enclosed within a housing or packaging. During the fabrication process, the packaging is usually sealed along the peripheral edges of the cell, thereby forcing like leads together. In most battery designs opposite leads are offset from each other so that they will not contact each other. Like leads, such as two cathode sections, are typically forced together and joined. It is at these locations where the burrs or shards are more likely to penetrate through the separator layers and short circuit the cell by coming into contact with layers of the opposite polarity.
The present invention overcomes this problem by providing a protective layer on the leads of the current collector where the leads extend from the cell to prevent burrs or shards on the current collectors from penetrating through the separator layer.
In accordance with the present invention, there is provided a Li-ion cell comprised of an anode layer, a cathode layer and a separator layer that is disposed between the anode layer and the cathode layer. A first, planar metal mesh layer is adjacent the anode layer. The first metal mesh layer has a coplanar tab extending beyond the separator layer to define a negative lead. A second, planar metal mesh layer is adjacent the cathode layer. The second metal mesh layer has a coplanar tab extending beyond the separator layer to form a positive lead. A first protective layer is applied on the coplanar tab of the first metal mesh layer. The first protective layer is disposed where the tab extends beyond the anode layer and is disposed on the surface of the tab facing the second metal mesh layer. A second protective layer is applied on the coplanar tab of the second metal mesh layer. A second protective layer is disposed where the tab extends beyond the cathode layer and is disposed on the surface of the tab facing the first metal mesh layer.
In accordance with another aspect of the present invention, there is provided a Li-ion cell, comprised of a first cathode section and a second cathode section. Each cathode section has a cathode current collector in contact therewith. The cathode current collector is comprised of a sheet of metal mesh having a tab portion that extends outwardly from the sheet beyond the cathode section to form a cathode section lead. The cathode section lead from the first cathode section is disposed adjacent to the cathode section lead from the second cathode section. An anode section is disposed between the cathode sections. The anode section has an anode current collector having a tab portion that extends therefrom beyond the anode section to form an anode section lead. A separator layer is disposed between the anode section and each of the cathode sections. A protective layer is applied to the tab portion of each cathode current collector where the tab portion extends from the sheet. The protective layers are disposed between the tab portions to prevent shorts when the tab portions are pressed together to form a single positive lead.
It is an object of the present invention to provide a Li-ion cell using metal mesh as current collectors.
It is another object of the present invention to provide a cell as described above that is less susceptible to failure from short-circuiting during fabrication.
Another object of the present invention is to provide a cell as described above having protective sleeves around the battery leads in the vicinity where the leads extend from the cell.
A still further object of the present invention is to provide a cell as described above having plastic tape surrounding each lead to isolate the lead from other battery components.
These and other objects and advantages will become apparent from the following description of a preferred embodiment of the invention, taken together with the accompanying drawings.